Randomizing entries on multiple input root files

ROOT
1

I have a set of input root files containing a single TTree whose structure is the same on all inputs. I want to create an output root file whose TTree entries are randomly ordered from those on the input.
The problem I am having is that when I try to randomly access the entries on the input TChain, the process is incredibly slow, apparently because the entries are not memory resident. In the version of root I am using (4.04), the method TChain::LoadBaskets() is not implemented.

I have tried using hadd to concatentate the input root files into a single root file. I am able to do this. There are no i/o errors in this process. I can also open the resulting root file and TTree->Draw() a branch. But when I try to run the global method TTree::LoadBaskets(), the error “R__unzip: error during decompression” occurs. How can I diagnose/work around this problem?

Thanks for any help you can provide on this.

Bill Lockman

2

Hi Bill,

It is likely that your merged tree is too big to fit in memory. R__Unzip fails because a memory buffer could not be allocated.

Rene